Hydraulic test rigs for durability tests are commonly used in the vehicle industry to test components of an automobile. For example, they serve to perform vibration tests and tests on the vehicle suspension and the steering mechanism. During a test run of a typical durability test, the component is subjected to a periodically repeated load for a predetermined time period. After the test run, the component is examined for changes or damages. The reference pattern of the load must be reproduced as accurately as possible to ensure well defined testing conditions. To this end, a feedback controller compares a reference curve with a feedback signal from a sensor in a thereby defined controlled system. Subsequently, the controller generates a control signal and sends the control signal to an actuator of the controlled system. Thereby, a control loop is defined which is also called a servo control loop.
In servo control loops, there is usually a control deviation between a reference signal and a feedback signal of the controlled system. This deviation is due to the transfer function or due to a disturbance reaction of the controlled system. The deviation may include overshoots, amplitude or phase errors.
Conventional servo control loops use a PID controller as a feedback controller. However, the quality of control for a conventional servo control loop is often not sufficient.
A known method to correct for the disturbance reactions in a test rig is therefore to perform a preliminary run of the test rig and to compute a corrected reference signal from this preliminary run. During the test run, the feedback controller uses the corrected reference signal instead of the original reference signal. This cumbersome method makes use of the repeated nature of a typical durability test.
Another known method is the use of an adaptive controller. The adaptive controller measures the system response. During a test run, the adaptive controller adapts its parameter settings accordingly. This method is able to compensate for some changes in the controlled system.